Stable dentifrices containing a monofluorophosphate, an insoluble metaphosphate, and calcium carbonate

ABSTRACT

Dentifrice composition containing a monofluorophosphate and polishing agent containing alkaline earth metal carbonate and insoluble alkali metal metaphosphate, alumina or mixture thereof. The ratio of carbonate to insoluble alkali metal metaphosphate is about 3:1 to about 1000:1 the ratio of calcium carbonate to alumina is about 1:3 to about 1000:1. This dentifrice retains a desirable level of soluble fluoride upon aging and when insoluble alkali metal metaphosphate is present, does not cause substantial corrosion of unlined aluminum containers.

United States Patent King et a1. 1 1 Feb. 4, 1975 [54] STABLE DENTIFRICES CONTAINING A 3,119,743 1/1964 Ericssonm; 424/52 MONOFLUOROPHOSPHATE, AN 1/1322 fianagan et a}. 251/25 INSOLUBLEMETAPHOSPHATE AND 3 624 199 11l1971 N i t'l ee t e t al uiiiiiii .11: 424l57 CALCIUM CARBONATE 3,634,585 1/1972 Manahan et a1. 424/52 [75] Inventors; wim James King, River Edge; 3,678,155 7/1972 Chppmgdale et a1 424/52 1 wff g g f FOREIGN PATENTS OR APPLICATIONS m; i n f 1,076,851 7/1967 Great Britain 424/52 N J a e 0 1,132,830 11/1968 Great Britain 424/52 [73] Assignee: Colgate-Palmolive Company, New P i E i Ri h d L Huff York, NY. Attorney, Agent, or Firm-Robert L. Stone; Murray [22] Filed: sept 9, 1971 M. Grill; Herbert S. Sylvester [21] Appl. No.: 176,396 7 [57] ABSTRACT Relted Application Data 7 Dentifrice composition containing a monofluorophos- [63] g g 2 3 N 2 phate and polishing agent containing alkaline earth f gg B 58;? 1 2 metal carbonate and 1nso1uble alkah metal metaphosan one phate, alumina or mixture thereof. The ratio of carbonate to insoluble alkali metal metaphosphate is about 3:1 to about wood the ratio of calcium carbon 878 241 ate to alumina is about 1:3 to about 100011. This denle 0 earc tifrice retains a desirable level of soluble fluoride upon aging and when insoluble alkali metal metaphosphate [56] SS SE 'fg is present, does not cause substantial corrosion of unlined aluminum containers.

3,060,098 10/1962 Gershon 424/52 3,095,356 5 Claims, N0 Drawings- 6/1963 Moss 424/52 l STABLE DENTIFRICES CONTAINING A MONOFLUOROPHOSPHATE, AN INSOLUBLE METAPI'IOSPHATE, AND CALCIUM CARBONATE This application is a continuation of Ser. No. 878,241, filed Nov. 19. 1969, which is a continuationin-part of Ser. No. 785,731, filed Dec-20. 1968. both now abandoned.

The present invention relates to a dentifrice preparation containing a water-soluble monofluorophosphate salt.

Water soluble monofluorophosphates and particularly alkali metal monofluorophosphates such as sodium monofluorophosphate have been used as fluorine-providing active ingredients in dentifrice compositions. The polishing agents which may be used in such dentifrices have been the subject of much investigation.

A dentifrice containing sodium monofluorophosphate and a polishing agent which is free of insoluble phosphate salt and which, in fact, is solely calcium car- 2 used in any suitable purity provided that any impurities do not substantially adversely affect the desired properties. In general, the purity is desirably at least about 80 percent. For best results, it should be at least 85 percent, and preferably at least 90 percent by weight of sodium monofluorophosphate with the balance being primarily impurities or by-products of manufacture such as sodium fluoride, water-soluble sodium phosphate salt. and the like. Expressed in another way, the sodium bonate loses an appreciable amount of the fluorine in solution upon aging.

ln order to obtain maximum effect of the monofluorophosphate. the prior art' has used but minor amounts of calcium salt, such as dicalcium phosphate or calcium carbonate, or magnesium salt, and has usedas the major polishing agent, insoluble alkali metal metaphosphate. It has been the general practice in the prior art to package monofluorophosphate dentifrices in an epoxy lined aluminum container or in lined containers of other metals or in plastic containers since components of various monofluorophosphate dentifrices cause corrosion of unlined aluminum tubes upon storage.

This invention provides monofluorophosphate dentifrice which has special advantages over prior art monofluorophosphate dentifrices containing calcium carbonate or insoluble alkali metal metaphosphate'More particularly, the dentifrice of the instant invention eliminates the instability characteristic of prior art monofluorophosphate dentifrice containing calcium carbonate which is free of insoluble phosphate. The invention also provides a monofluorophosphate dentifrice which upon storage-does not cause substantial corrosion of unlined aluminum containers.

Other desirable properties will be apparent from consideration of the following specification.

In accordance with certain of its aspects, this invention relates to a dentifrice composition comprising a water-soluble monofluorophosphate and a waterinsoluble compatible polishing material comprising a mixture of alkaline earth metal carbonate and insoluble alkali metal metaphosphate, the ratio of said carbonate to said insoluble alkali metal metaphosphate beingabout 3:1 to about 100021.

In accordance with certain of its additional aspects, this invention relates to a packaged dentifrice composition comprising an unlined aluminum container and in contact with said container a dentifrice composition comprising a water-soluble monofluorophosphate and a water'insoluble compatible polishing material which comprises a mixture of alkaline earth metal carbonate and insoluble alkali metal metaphosphate, the ratio of said carbonate to said insoluble alkali metal metaphosphate being about 3:1 to about 100021.

The sodium monofluorophosphate as commercially available may vary considerably in purity. It may be monofluorophosphate employed should have a total fluoride content of above 12 percent. preferably above 12.7 percent; a content of not more than 1.5 percent. preferably not more than 1.2 percent of free sodium fluoride; and a sodium monofluorophosphate content of at least 12 percent, preferably at least 12.1 percent, all calculated as fluorine.

Typically, the monofluorophosphates is present in amount which provides about 0.01 1 percent fluorine to the dentifrice. Thus, sodium monofluorophosphate is typically present in amount of about 0.05 percent to about 7.6 percent.

The alkaline earth metal carbonate of the polishing agent is magnesium carbonate or more preferably calcium carbonate (chalk). Chalk is typically employed in powder form of a size of about 1 to 10 microns.

It is preferred to use a grade of calcium carbonate of relatively high apparent specific gravity, say about 0.9 to 1.2. If desired, calcium carbonate grades of lower apparent specific gravity, say about 0.7 to 0.9, also may be used. Apparent specific gravity refers to the untamped specific gravity of the salt.

In accordance with certain aspects of this invention, the minor component of the polishing agent is an insoluble alkali metal metaphosphate.

The insoluble alkali metal metaphosphates are preferably the insoluble sodium and potassium salts of polymetaphosphoric acid. These materials are known in the art with the insoluble sodium'metaphosphate having been suggested as a polishing agent as previously indicated. Such materials may be formed in any suitable manner, as illustrated by Thorpes Dictionary of Applied Chemistry, vol. 9 (4th ed.), pp. 510-511. The forms of insoluble sodium metaphosphate known as Madrells salt and Kurrols salt are further examples of suitable materials. These metaphosphate salts exhibit only a minute solubility in water, and are commonly referred to as insoluble metaphosphates therefore. There is present a minor amount of soluble phosphate material as impurities, usually of the order of a few percent such as up to about 4 percent by weight. The amount of soluble phosphate material which is believed to be a soluble sodium trimetaphosphate in the case of insoluble sodium metaphosphate may be reduced by washing the water if desired. The insoluble alkali metal metaphosphate is typically employed in powder-form of a size such that no more than about 1 percent of the material is larger than about 37 microns.

The ratio of carbonate to insoluble alkali metal metaphosphate is about 311 to about 1000:1, preferably about 6:1 to about 500:1 and most preferably about 46.2511.

At the preferred ratios, particularly when relatively small amounts of insoluble alkali'metal metaphosphate are employed, the dentifrice does not corrode unlined aluminum tubes, almost without exception. When greater amounts of the metaphosphate are employed, within the scope of the invention, the dentifrice still I does not cause substantial corrosion of unlined aluminum tubes, although an exceptional case of some adverse action on the alumium may occasionally occur.

The total polishing agent content of the dentifrice is variable, but will generally be up to about 95 percent, by weight of the total composition. In the case of a dental cream, such polishing agents will generally be about 20 percent to about 75 percent, whereas in tooth powders the polishing agents will usually be in greater proportion, such as about 70 percent to about 95 percent.

In the preparation of tooth powders, it is usually sufficient to admix mechanically, for example, by milling. the various solid ingredients, in appropriate quantities and particle sizes.

Any suitable surface active or detersive material may be included in the dentifrice compositions. Such compatible materials are desirable to provide additional detersive, foaming and anti-bacterial properties depending upon the specific type of surface active material and are selected similarly. These detergents are watersoluble organic compounds usually, and may be anionic, nonionic or cationic in structure. It is preferred to use the water-soluble non-soap or synthetic organic detergents usually. Suitable detersive materials are known and include, for example, the water-soluble salts of higher fatty acid monoglyceride monosulfate detergent (e.g. sodium coconut fatty acid monoglyceride monosulfate), higher alkyl sulfate (e.g. sodium lauryl sulfate), alkyl aryl sulfonatee.g. sodium dodecyl benzene sulfonate), higher fatty acid esters of l,2-dihydroxy propane sulfonate (e.g. sodium coconut fatty acid ster of l,2-dihydroxy propane sulfonate), and the like.

The various surface active materials may be used in any suitablegamount, generally from about 0.05 to about percent by weight, and preferably from about 0.5 to 5 percent by weight of the dentifrice composition.

It is a further embodiment of the present invention to use the substantially saturated higher aliphatic acyl amides of lower aliphatic amino carboxylic acid compounds, such as those having 12 to l6 carbons in the acyl radical, and as more particularly described in US Pat. No. 2,689,170, issued Sept. 14, 1954. The amino acid portion is derived generally from the lower aliphatic saturated monoaminocarboxylic acids having about 2 to 6 carbons, usually the monocarboxylic acid compounds. Suitable compounds are the fatty acid amides of glycine, sarcosine, alanine, 3-amino-propanoic acid and valine having about 12 to 16 carbons in the acyl group. It is preferred to use the N-lauroyl, myristoyl and palmitoyl sarcoside compounds however for optimum effects.

The amide compounds may be employed in the form of the free acid or preferably as the water-soluble salts thereof, such as thealkali metal, ammonium, amine and alkylolamine salts. Specific examples thereof are sodium and potassium N-lauroyl, myristoyl and palmitoyl sarcosides, ammonium and ethanolamine N-lauroyl sarcoside, N-lauroyl sarcosine, and sodium N-lauroyl glycide and alanine. For convenience herein, reference to amino carboxylic acid compound, sarcoside," and the like refers to such compounds having a free carboxylic group or the water-soluble carboxylate salts.

Such materials are utilized in pure or substantially pure form. They should be as free as practicable from soap or similar higher fatty acid material which tends to reduce the activity of these compounds. In usual practice,'the amount of such higher fatty acid material is less than percent by weight of the amide and insufficient to substantially adversely affect it, and preferably less than about 10 percent of said amide material. 5 ln dental cream formulations, the liquids and solids should be proportioned to form an extrudable creamy mass of desirable consistency. In general, liquidsin the dental cream will comprise chiefly water. glycerine, sorbitol. propylene glycol, or the like, including suitable mixtures thereof. It is advantageous usually to use a mixture of both water and a humectant or binder such as glycerine or sorbitol. It is preferred to use glycerine. The total liquid content will generally be about 20 75 percent by weight of the formulation. It is preferred to use also a gelling agent in dental creams such as the natural and synthetic gum and gum-like material. e.g. lrish moss, gum tragacanth,- sodium carboxymethylcellulose, polyvinylpyrrolidone, starch, and the like. The Irish moss and sodium carboxyme'thylcellulose are compatible particularly and are preferred gelling .agents as illustrated. The gum content is usually in an amountup to about 10 percent and preferably about" 0.5 5 percent by weight of the formulation.

In accordance with certain additional aspects of this invention, desirable aging characteristics are obtained when a minor amount of hydrated aluminum oxide (alumina) is in the dentifrice preparation as part of the polishing agent together with alkaline earth metal carbonate. The ratio of carbonate to alumina is about 1:3 to about lOOO: l. If desired, insoluble alkali metal meta-v phosphate may also be a component of the polishing agent. The ratio of the carbonate to insoluble alkali metal metaphosphate being about 3:l to about 1000: l. Dentifrices containing small amounts-of insoluble alkali metal methaphosphate, say where the ratio of calcium carbonate to the metaphosphate is more than 10021, have better aging characteristics when alumina is also present.

A dental. cream having improved physical properties may be prepared from alkaline earth metal carbonate and optionally insoluble alkali metal metaphosphate suspended in a gel comprising water, humectant and gelling agent, with said fluoride compound and organic non-soap synthetic detergent, and hydrated aluminum oxide, said dental cream having pH from about 7 to 9.5. If insoluble alkali metal metaphosphate is present, the hydrated aluminum oxide may be omitted. These dental creams exhibit a superior degree of stability to aging for long periods'of time, particularly at elevated temperatures. The aluminum oxide acts as a stabilizing and modifying agent so as to eliminate or inhibit any tendency for separation or syneresisof the dental cream in the collapsible tube.

The preferred ratio of alkaline earth metal'carbonate to alumina is about 32-1 to 10011, and most preferably about 35:1 to about 521l.

In the instant invention sufficient insoluble alkali metal metaphosphate and/or alumina is present to substantially prolong the period of time during which the monofluorophosphate remains substantially soluble, e.g., to insure that at least, and preferably more than, about 40 percent, and most preferably at least about 50 percent, of the original monofluorophosphate content remains soluble after accelerated aging of the dentifrice for nine weeks at 49C.

Suitable examples of hydrated aluminum oxide which may be employed are the forms known as alpha and beta aluminum oxide trihydrate and mixtures thereof. It is used usually in the form of fine particles of any desired particle size in the manufacture of the dental cream. In practice, it is preferred to use the alpha trihydrate form of which at least about 90 percent of the particles pass through on a U5. standard No. 325 mesh sieve and not more than about 5 percent of the particles by weight are less than 5 microns. It has been found that amounts of hydrated aluminum oxide from about one'fourth to about l percent by weight are most desirable and preferably about l percent by weight of the dentifrice composition. Various other materials may be incorporated in the oral preparations of this invention. Examples thereof are coloring or whitening agents, preservatives, silicones, chlorophyll compounds, ammoniated materials such as urea, diammonium-phosphate and mixtures thereof, and other constituents. These adjuvants are incorporated in the instant compositions in amounts which do not substantially adversely affect the properties and characteristics suitably selected and used in proper amount depending upon the particular type of preparation involved.

For some purposes it may be desirable to include antibacterial agents in the compositions of the present invention. Typical antibacterial agents which may be used in amounts of about 0.0l percent to about percent, preferably about 0.05 percent to about 1.0 percent, by weight of the dentifrice composition include:

N'-4(chlorobenzyl)-N-2,4-

dichlorobenzyl)biguanide;

p-chlorophenyl biguanide;

4-chlorobenzhydryl biguanide;

4-chlorobenzhydrylguanylurea;

N-3-lauroxpropyl-N -p-chlorobenzylbiguanide;

l,6-di-p-chlorophenylbiguanidohexane;

l-(lauryldimethylammonium)-8-(p-chlorobenzyldimethylammonium) octane dichloride; 5,6-dichloro-2-guanidinobenzimidazole;

N'-p-chlorphenyl-N -laurylbiguanide;

S-amino-l ,3-bis(2-ethylhexyl)-5-methylhexahydropyrimidine; and their non-toxic acid addition salts.

Any suitable flavoring or sweetening materials may be employed in formulating a flavor for the compositions ofthe present invention. Examples of suitable flavoring constituents include the flavoring oils, e.g. oils of spearmint, peppermint, Wintergreen, sassafras. clove, sage, eucalyptus, marjoram, cinnamon, lemon and orange, as well as sodium methylsalicylate. Suit able sweetening agents include sucrose, lactose, maltose, sorbitol, sodium cyclamate and saccharine. Suitably, flavor and sweetening agent may together comprise from about 0.01 to 5 percent or more of the compositions of the instant invention.

The dental creams should have a pH practicable for use. A neutral to basic pH is particularly desirable. The initial pH range of about 7 to 9.5 preferably 7.5, is considered the most practicable for use. Where reference is made to pH herein, it is intended that such pH determination be made on the dental cream directly. If necessary, basic materials may be added to adjust the pH as desired.

The container in which the dentifrice composition is placed is typically a tube from which the dental cream can be extruded. A particularly desirable aspect of the invention is the fact that the dentifrice composition including insoluble alkali metal metaphosphate can be desirably packaged in an unlined aluminum container and exhibit desirable cosmetic and rheological properties upon storage without causing substantial layer formation or corrosion of the aluminum with which it is contacted.

The most desirable results have been obtained when the dentifrice contains about 0.l to 3 percent by weight of insoluble alkali metal metaphosphate and about 44 percent to 47 percent by weight of calcium carbonate.

The following specific examples are further illustrative of the nature of the present invention. but it is to be understood that the invention is not limited thereto. The compositions are prepared in the usual manner and all amounts ofthe various ingredients are by weight unless otherwise specified.

EXAMPLE I The following dental creams are prepared:

Parts Sodium monofluorophosphate 0.76 0.76 Calcium carbonate 52.00 46.25 Insoluble sodium mctaphosphate 1.00 Glycerinc 22.00 22.00 Sodium carboxymcthylccllulosc 0.95 L30 Hydrated alumina 1.00 Sodium N-lauryl sarcosinate 2.00 2.00 Sodium bcnzoate 0.50 0.50 Sodium saccharine 0.20 0.20 Flavor 0.90 0.90 Water as to I00 q.s. to I00 Composition A in which no phosphate salt polishing agent is present and calcium carbonate is the sole abrasive and Composition B containing calcium carbonate, alumina and phosphate salt are aged at 49C. and the percentage of soluble monofluorophosphate present as fluoride is determined periodically. Each three weeks under this aging condition corresponds to about ones year aging at room temperature. The results are indicated in the table below:

'7 Soluhlc Monofluorophosphate Fluoride 49C.

Weeks Composition 0 3 6 9 A 0.09 0.07 0.03 0.0l B 0.09 0.08 0.08 0.07

Thus, it is clear from these results that the addition of a small amount of the insoluble metaphosphate and alumina markedly increases the ability of Composition B to retain soluble fluorine.

When Composition B is placed in an unlined aluminum tube, the aluminum surface in contact with the dentifrice remains substantially free from corrosion even over a prolonged period of time.

EXAMPLE 2 The following dentifrices also have high retention of soluble fluorine and do not cause a substantial degree of corrosion of the aluminum surface with which they are contacted in unlined aluminum tubes.

C D E Sodium monofluorophosphate 0.76 0.76 0.76 Calcium carbonate 40.l 44.25 47. l 5 lnsolublc sodium metaphosphate 7.10 3.00 0. l0 Glycerine 22.00 22.00 22.00 Sodium carhoxymethylcellulose L L L30 Hydrated alumina L00 1.00 [.00 Sodium N-lauryl sarcosinate 2.00 2.00 2.00 Sodium bcnzoate 0.50 0.50 0.50 Sodium saccharine 0.20 0.20 0.20 Flavor 0.90 0.90 0.90 Water q.s. q.s. q.s.

to I00 to I00 to I00 EXAM PLE 3 The following dentifrices are also within the scope of the invention:

Parts F (i H Sodium monofluorophosphatc 0.76 0.76 0.76 Calcium Carbonate 35.25 47.20 46.00 lnsoluble sodium metaphosphate l2.00 0.05 L00 Glycerine 22.00 22.00 22.00 Sodium carboxymcthylccllulosc L20 L30 L30 Hydrated alumina L00 L00 Sodium N-lauroyl sarcosinate 2.00 2.00 2.00 Sodium benzoate 0.50 0.50 0.50 Sodium saccharine 0.20 0.20 0.20 Flavor 0.90 0.90 0.90 Water q.s. q.5. q.s.

to 100 to 100 to I00 EXAMPLE 4 The following dentifrices are prepared:

l J K glycerinc 22.00 22.00 22.00 Sodium Bcnzoate 0.50 0.50 0.50 Sodium saccharine 0.20 0.20 0.20 Sodium monofluorophosphate 0.76 0.76 0.76 Hydrated alumina 52.00 1.00 Calcium carbonate 52.00 52.00 Sodium carboxymcthyl cellulosc 0.95 0.95 0.95 Sodium N-lauroyl sarcosinatc 2.00 2.00 2.00 Flavor 0.80 0.80 0.80 Water (4.5. q.s. q.s.

to 100 to I00 to 100 Each of the dentifrices are aged at 49C. with the percentage of monofluorophosphate determined periodically. The results are indicated in the table below:

7:. Soluble Monofluorophosphatc Thus, it is clear that composition K retains soluble fluorine better than compositions l and J.

EXAMPLE 5 The following dentifrices are also within the scope of the invention:

Parts L M N Sodium monofluorophosphatc 0.76 0.76 0.76 Glycerinc 22.00 22.00 22.00 Sodium benzoatc 0.50 0.50 0.50 Sodium saccharine 0.20 0.20 0.20 Hydrated alumina l3.00 26.00 39.00 Calcium carbonate 39.00 26.00 13.00 Sodium carboxymcthyl cellulose 0.95 0.95 0.95 Sodium N-lauroyl sarcosinatc 2.00 2.00 2.00 Flavor 0.140 0.80 0.80 Water q.s. q.s. (1.5.

to I00 to I00 to I00 EXAMPLE 6 The following dentifrices are also within the scope of the invention:

In addition to sodium monofluorophosphate, Na PO F, other monofluorophosphate salts which have sufficient water solubility for use in the instant invention include calcium monofluorophosphate. magnesium monofluorophosphate and aluminum monofluorophosphate. In accordance with this invention the term monofluorophosphate also includes monofluoropolyphosphates such as Na P,-,O F, K P O F, (NH4)4P3O1;F, NagKpgoyF, (NH4)3N3P309F and Ll 3 9 lt will be apparent to one skilled in the art that modifications of the above examples may be made thereto.

We claim:

1. A packaged dentifrice composition comprising an unlined aluminum container and in contact therewith a dentifrice composition comprising a water-soluble monofluorophosphate in amount which provides about 0.0l-l% by weight fluorine to the dentifrice and about 20-95% by weight of a water-insoluble compatible polishing material consisting essentially of a mixture of calcium carbonate and an insoluble alkaline metal metaphosphate wherein the ratio of said carbonate to said metaphosphate is about 3:l to about 1.00021.

2. The packaged dentifrice claimed in claim 1 wherein the ratio of said carbonate to said metaphosphate is about 6:l to about 500:L

3. The packaged dentifrice claimed in claim I wherein said water-soluble monofluorophosphate is sodium monofluorophosphate and said insoluble alkali metal metaphosphate is insoluble sodium metaphosphate.

9 l 4. The dentifrice composition claimed in claim 3 wherein the ratio of said calcium carbonate to said inwherein the ratio of said calcium carbonate to said insoluble sodium metaphosphate is about 6:] to about soluble sodium metaphosphate is about 46.25:l. lOOOcl.

5. The dentifrice Composition claimed in claim 3 v 

1. A PACKAGED DENTIFRICE COMPOSITION COMPRISING AN UNLINED ALUMINUM CONTAINER AND IN CONTACT THEREWITH A DENTIFRICE COMPOSITION COMPRISING A WATER-SOLUBLE MONOFLUOROPHOSPHATE IN AMOUNT WHICH PROVIDES ABOUT 0.01-1% BY WEIGHT FLUORINE TO THE DENTRIFRICE AND ABOUT 20-95% BY WEIGHT OF A WATER-SOLUBLE COMPATIBLE POLISHING MATERIAL CONSISTING ESSENTIALLY OF A MIXTURE OF CALCIUM CARBONATE AND AN INSOLUBLE ALKALINE METAL METAPHOSPHATE WHEREIN THE RATIO OF SAID CARBONATE TO SAID METAPHOSPHATE IS ABOUT 3:1 TO ABOUT 1,000:1.
 2. The packaged dentifrice claimed in claim 1 wherein the ratio of said carbonate to said metaphosphate is about 6:1 to about 500:1.
 3. The packaged dentifrice claimed in claim 1 wherein said water-soluble monofluorophosphate is sodium monofluorophosphate and said insoluble alkali metal metaphosphate is insoluble sodium metaphosphate.
 4. The dentifrice composition claimed in claim 3 wherein the ratio of said calcium carbonate to said insoluble sodium metaphosphate is about 46.25:1.
 5. The dentifrice composition claimed in claim 3 wherein the ratio of said calcium carbonate to said insoluble sodium metaphosphate is about 6:1 to about 1000:1. 